While putting together the engine and setting up the Jesel Belt Drive, I needed to check Top Dead Center (TDC) and when I went to look for my tool to screw into the spark plug hole, I couldn’t find it.  So it was time to make a new one.

Last time I took the trouble to modify an old spark plug knocking out the porcelain, and welding a bolt to the end which was frankly a pain in the ass with the time it takes. Porcelain doesn’t knock out of a spark plug real easy.

I quick trip to the local O’Rielly’s didn’t turn up a regular tool for this, but I did find some 14mm spark plug anti-foul adapters. These things are made as a spark plug extension (Wonder if they work?), but for this project they work great to modify for a spark plug stop. A big plus is they aren’t very hard, making it somewhat easy to thread a bolt down in it.

I drilled the center out and tapped it for 3/8-16 NC, then got a piece of all-thread and smoothed the nose so it won’t mark the piston.  Presto, instant piston stop and it’s easy to make in a few minutes without having to drag the welder out.

For those that haven’t used one of these before, you screw this into #1 cyl. Then put a degree wheel on the crank, rotate the engine clockwise slowly till it hits the bolt. Then mark the degree wheel where that position is at. Then, rotate the crank counter-clockwise (slowly!) again till it hits the bolt. Mark the degree wheel at this location.

The engine Top Dead Center (TDC) position is half the way between those two locations you marked on the degree wheel.

Home Made Tools Piston Stop TDC